Electron microscope structure



May 13, 1947. c. H. BACHMAN ELECTRON MICROSCOPE STRUCTURE Filed April27, 1944 m .m W m o B z H t e A .m 7

Patented May 13, 1947 UNITED STATES ELECTRON MICROSCOPE STRUCTURE 7Charles H. Bachman, Scotia, N. Y., assignor to General Electric Company,a corporation of New York Application April 27,

3 Claims.

My invention relates to electron microscope structure and in particularto a new and improved apparatus for introducing specimens to be examinedinto an evacuated electron microscope chamber.

It has long been a problem in electron microscopy to obtain suitablmeans for introducing specimens into an evacuated chamber. In the usualpractice, substantial loss of vacuum results Whenever change inspecimens is made. Substantial improvement. in operating conditions andalso substantial decrease in time between subsequent observations may beexpected if specimens may be introduced both without loss of vacuum andwithout shutting down the vacuum system used and disconnecting the powersupply. Accordingly, it is an object of my invention to provide a newand improved specimen insertion apparatus for electron microscopes bywhich specimens may be replaced without substantial loss of Vacuumwithin the main microscope chamber.

Another object of my invention is to provide a new and improved specimeninsertion apparatus for an electron microscope which is sealed by aslide containing the specimen to be observed.

It is a still further object of my invention to provide a new andimproved electron microscope structure in which specimens to be observedmay be changed without removing the power supplied to the electrodes ofthe microscope.

One of the features of my invention consists of the use in an electronmicroscope of a thin specimen-carrying slide which fits into a narrowslot in a resiliently supported member, the slide serving to close theslot and seal the evacuated chamber of the microscope from atmosphericpressure. The resilient mounting of the slide-carrying member permitsadjustment of the specimen by means of a manipulator so that it lies inthe path of an electron beam and is traversed by the beam to obtain amagnified picture of the specimen.

Another object of my invention is to provide a new and improved electronmicroscope structure in which no valves are required for insertingspecimens to be examined into a vacuum chamber and in which a vacuumpump is operated continuously while a specimen is being inserted.

The features of the invention which are desired to be protected hereinare pointed out with particularity in the appended claims. The inventionitself, together with further objects and advantages thereof may best beunderstood by reference to the following description taken in connectionwith the drawing in which Fig. 1 represents a cross-sectional view of anelectron microscope suitably embodying the invention and Fig. 2 is aview of the specimen-carrying slide employed in the microscope structureof Fig. 1.

Referring particularly to Fig. 1, there is shown 1944, Serial No.532,978

an electron microscope comprising an elongated vacuum-tight containerwhich consists mainly of a cylindrical metal part l closed at one end bya transverse glass wall 2 which is provided on its inner surface with ascreen 3 coated with fluorescent particles and adapted to form an imageunder the impact of lectrons. At the opposite end of the microscopethere is provided a glass insulating structure 4 which serves to supportan electron source in the form of a filamentary cathode 5. The cathode 5is surrounded by an apertured cup-shaped member 6 having a narrow slitor opening I which confines the emitted electrons to a narrow beam andwhich is cooperatively positioned with respect to a diaphragm 8supported in contact with the main envelope part I. In the normal use ofthe apparatus, the envelope l and the electrode 8 are maintained atground potential, while the cathode is held at several thousand voltsbelow ground by a potential source, represented by the battery 5, sothat electrons emitted from the cathode are projected toward the window2.

Between the cathode 5 and the image reproducing screen 3 there isprovided an object or specimen supporting means which comprises a smalltube Ill extending into the envelope I and which is resilientlysupported from a neck portion H connected to envelope I by means of aflexible sealing member l2. The member l2 may comprise, for example, aSylphon bellows or a corrugated rubber sleeve. The tube In, which may beformed of metal, is provided with a longitudinal rectangular slot I3which is open at its upper end to the atmosphere and which is closed atits bottom end by a rounded portion M of the tube I 0. Removablysupported within the slot I3 is a slide or specimen holder l5 which ismachined to provide a precision fit within the slot I3. The slide orspecimen carrier l5, as shown in Fig. 2, is an inverted L-shaped member,the leg portion l6 of the L providing means for withdrawing the slidefrom the slot l3. Near its lower end the slide [5 is provided with anaperture ll 45 in which is positioned a supporting screen l8 on whichmay be placed a specimen to be observed. Near its lower end the metallicmember Ii) is provided with a transverse aperture comprising two tinyholes I9 which are opposite to each other 50 and open to the slot IS insuch a position that an electron beam coming from the cathode 5 passesthrough the openings l9 in the metallic member I!) to transradiate anobject supported on the screen I8 of the slide Hi.

There is also provided a manipulator 20 which may be operated by meansof a linkage 2| and an external operating means, not shown, to contactthe resiliently mounted tube ID to adjust the position of the lowerportion of the tube so 50 that the openings l9 and the opening [1 in theslide l5 fall in the path of the electron beam passing between thecathode 5 and the fluorescent screen 3. Such amanipulator maybe of thetype described in my joint copending application Serial No. 468,676,filed December 11, 1942, and assigned to the same assignee as thepresent application. The manipulator 20 may be used to move theapertures [9 in three'mutually perpendicular directions to position thespecimen to be examined in the path of the electron beam of themicroscope and in a desired position with respect to the electron lenssystem now to be described.

Between the specimen tube l and the screen 3 there are provided one ormore electron lens systems for exerting a refractive force upon theelectron rays proceeding from the specimen-under investigation. Whilethese lens systems may be of the magnetic or electrostatic type or anycombination of these two types, they are shown in Fig. 1 as being of theelectrostatic type-and comprise a pair of apertured metal diaphragms 22,2-3, which are maintained at ground potential by a connection to theenvelope I, and an intermediate diaphragm 24, which is insulated fromthe member ID and connected to the cathode potential by means of alead-in conductor 25 which extends through an insulating bushing 26. Thechamber I of the microscope structure may be evacuated by any suitablemeans, such as a vacuum pump, notshown, connected to'a tubulation 21formed in the walls of the metallic container I-.

In the operation of .my electron microscope, a specimen to be observedis placed-on the screen i8 within the slide 15 and the slide is insertedin the slot 13 of the tube 1 0. By means of the manipulator 20 the holesI9 and the specimen are positioned so that an electron beam coming fromthe cathode passes through the two small holes [9 to transradiate thespecimen and then enters into the electron lens. The electron beam isrefracted by the electron lens and passes onto the fluorescent screen 3to form an enlarged image of the specimen under observation. The imageon the fluorescent screen may be :further enlarged by means of a lightmicroscope which is represented generally as the lens 28 located outsideof the electron microscope in front of the end window -2. The smallholes I9 opening into the vacuum chamber are of the order of a few milsin diameter and, together with the long leakage path iormed between thewalls of the slot l3 and the slide machined to make -a close fit tothese walls, are made to constitute such a slow leak of air that novalves or looks are necessary and the vacuum pumps used for evacuatingthe chamber I need never be disconnected from the chamber even when theslide 1 5 is withdrawn. -By utilizing a plurality of slides and quicklyinserting a new slide when one is withdrawn from the slot 13, not onlyisli-t unnecessary to shutoff vacuum pumps-,but also thetpotent-ialsapplied to the cathode and the electron lens system may be leftconnected during a specimen insertion period.

It is apparent, therefore, that by this improved construction thecustomary valves and locks used in electron microscopy are eliminatedand the operation of an electron microscope to permit examination ofebjects-is expeditedto the extent that vacuum conditions are maintainedalmost continuously and no shutdown is required for changing specimens.Likewise potentials may be applied continuously to the electrodes of themicroscope.

While I have shown a particular embodiment of my invention, it will ofcourse be understood that I do not wish to be limited thereto sincevarious modifications may be made, and I eontemplate by the appendedclaims to cover any such modifications as fall within the true spiritand scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. An electron microscope comprising an evacuated chamber, means withinsaid chamber for projecting an electron beam, and means for supportingan object to be examined in the path of said beam, sa-idmeans'com-prising -a tubular mem. ber extending into said chamber, saidmember having a longitudinal slot therein and a transverse aperturecommunicating with said slot and positioned in the path of said beam,a-slide mem ber adapted to lit in said slot and support a specimen to beobserved across said aperture, said aperture being minute in size andsaid aperture and said slot forming a slow air leak between the innerand outer surfaces of said chamber when said slide is removed from saidslot.

2. The combination, in an electron microscope having an evacuatedchamber, of a flexibly mounted member extending into said chamber, saidmember having a longitudinal slot therein and -a transverse aperturecommunicating with said slot, means for positioning said member to placesaid aperture in alignment with an electron beam of said microscope,said aperture being minute in size and said aperture and said slotforming a long leakage path between the inner and outer surfaces of saidchamber having a slow rate of leakage, and a specimen carrier adapted tofit into said slot and to place a specimen to be observed across saidaperture, said carrier having a-closefit with the walls of said slot toblock substantially air flow through said'path.

3. A specimen support for an electron microscope having an evacuatedchamber comprising a tubular member extending into said chamber, saidmember having a longitudinal slot and a transverse aperturecommunicating with said slot, aslide adapted to fit in said slot and toprevent leakage of air through said slot and said aperture when inposition, said slide having a hole in alignment with said aperture andsaid aperture being of minute siZe and said slot being of suflicientlength to form a slow leakage path for air between the inner and outersurfaces of said chamber during periods when said slide is removed fromsaid slot.

CHARLES H. BACHMAN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,220,973 Marton Nov. 12, 1940 54-20 Krause .Nov, 25, 1941 2,272,843 Hillier Feb. 10, 1942 2,264,210Krause Nov. 25, 1941

